Ultra-high purity ammonia (NH3) is used in the electronics industry for integrated circuit (IC) and light emitting diodes (LED) manufacturing. Water is one of the major contaminants that must be removed to a concentration of 40 parts per billion (ppb) or less. Even though such low concentrations of water can be achieved in the ammonia manufacturing process, contamination is possible during subsequent shipping, handling, or at the point of use. There is a need for a point-of-use purifier (for bulk streams) or built-in purifier (for cylinders) including a drying agent to insure that water concentration is at 40 ppb and generally less before being used.
There are a number of physical and chemical adsorption methods in the prior art for removing water and other oxygen-containing impurities from hydride gases such as ammonia and inert gases. The following patents and articles are representative of the prior art.
U.S. Pat. No. 5,536,302 teaches a process for removing trace levels of oxygen from an inert gas, e.g., nitrogen and oxygen, via an adsorbent comprised of a porous reducing support impregnated with an alkali metal oxide or alkaline earth metal oxide of about 10 to 90% by weight. The oxides are formed from metal salts, such as, nitrates, acetates, benzoates, lactates, etc., the metals including cesium, sodium, potassium, and barium.
WO 97/06104 discloses a process for removing oxygen from ammonia via a getter material comprised of metallic iron and manganese present in a weight ratio of 7:1 and 1:1. Moisture is removed downstream of the oxygen removal process, by contact with a drying material. Examples of drying materials include barium oxide, calcium oxide, strontium oxide, or 3A zeolites.
U.S. Pat. No. 6,461,411 discloses a process for removing trace impurities, e.g., carbon dioxide and water to ppb and ppt levels from matrix hydrides, inert gases, and non-reaction gases including ammonia, phosphine, and arsine, etc., by contact with an activated gas purifier comprised of thermally activated unmodified organic aluminas and thermally activated modified inorganic aluminas under an inert gas. Modified aluminas are formed by treating the organic and inorganic aluminas with a basic salt such as oxides, hydroxides, carbonates, acetates, or oxalates of Group IA or IIA metals.
U.S. Pat. No. 6,241,955 discloses a method of removing gaseous contaminant, e.g., oxygen and water, from a hydride gas by contacting the gas stream with a quantity of high surface area reduced metal oxide, which is in an oxidation state which is less than its maximum and but not lower than its lowest oxidation state. Oxides such as manganese or molybdenum oxides are preferred although oxides of barium, calcium, iron, lithium, potassium, rhenium, sodium, strontium, titanium, tungsten, and vanadium can also be used.
Japanese Patent 9-142833 discloses removal of water from ammonia by contacting the gas with an adsorbent comprising BaO, or a mixture containing BaO and CaO with BaO as the major compound, whereby water is removed through a chemical reaction with the metal oxide.
EP 1,176,120 discloses a process for removing water and other impurities to a level of less than 0.1 ppm from ammonia by contacting the ammonia with an adsorbent having manganese oxide and/or nickel oxide as an active ingredient on a porous support and thereafter with a zeolite. The adsorbent is prepared by reducing the metal oxide in hydrogen at temperatures greater than 500° C. for manganese and up to 350° C. for nickel. The ammonia may further be passed through a bed of synthetic zeolite with a pore diameter between 4 to 10 angstroms to remove oxygen, carbon dioxide, and moisture.
EP 0 484,301 B1 and 0 470,936 B1 describe processes for removing oxygen and other impurity gases from ammonia by the use of hydrogenated getter metal alloys comprised of varying amounts of zirconium (Zr), vanadium (V) and iron (Fe) with a preferred composition of 70% Zr, 24.6% V, and 5.4% Fe.
U.S. Pat. No. 6,110,258 and U.S. Pat. No. 6,395,070 disclose a method for removing water from a gas, particularly acid gases by contacting the gas with a zeolite that has a silica to alumina ratio above about 10. Prior to contact, the zeolite is heated to a temperature above 650° C. prior to contacting it with the gas.
U.S. Pat. No. 4,963,363 describes an apparatus for removing water, oxygen and other impurities from various gases such as arsine, phosphine, and ammonia by contact with a scavenger including a high surface area support with anions that are reactive towards the impurities.
U.S. Pat. No. 5,531,971 discloses a process for purifying gas streams such as hydrogen, hydride gases, and nitrogen by contact with a pyrolyzed metal scavenger deposited on a polymeric or macroreticulate polymer support. The pyrolyzed metals are selected from Group IA of the Periodic Table.
Physical adsorption by zeolites such as A and X has also been widely used as a means for removing water. These physical adsorbents are effective and have good capacity for inert gas purification. However, their efficiency and capacity for water removal from ammonia and other hydride gases are not sufficient. Accordingly, new adsorbents for effecting the removal of water are desired.